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Progress and Challenges of Semiconducting Materials for Solar Photocatalysis
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Optical Properties and Applications of Semiconductors, 2023
Mridula Guin, Tanaya Kundu, Vinay K. Verma, Nakshatra Bahadur Singh
Photocatalysts can be sorted into two different classes: homogeneous and heterogeneous photocatalysts. Transition metal complexes are used as homogeneous photocatalysts while semiconducting materials are primarily used as heterogeneous photocatalysts. Semiconductors have some special characteristics that include beneficial electronic structures, light absorption characteristics, charge carrying properties and well-matched lifetime in the excited state. Heterogeneous photocatalysis is more preferred over the homogeneous photocatalysis as it is an economical method because of its requirement of ambient temperature and pressure conditions. A good semiconductor photocatalyst should maintain the following characteristics (Nakata and Fujishima 2012): (1) photo chemical activity, (2) absorb visible or UV light, (3) photostable and photon non-corrosive, (4) low cost, (5) safe for the environment and (6) chemically and biologically unreactive.
Introduction to Borate Phosphors
Published in S. K. Omanwar, R. P. Sonekar, N. S. Bajaj, Borate Phosphors, 2022
Pritee K. Tawalare, A. B. Gawande
The luminescent system generally consists of a host lattice and a luminescent centre, often called an ‘activator’. In general, the host needs to be transparent to the radiation source used for the excitation process. The activator absorbs the exciting radiation and is raised to an excited state. The excited state returns to the ground state by emission of radiation or by non-radiative decay. It is necessary to suppress this non-radiative process. In some materials, the excitation radiation is not absorbed by the activator but the other ion may absorb the exciting radiation and subsequently transfer it to the activator. In this case, the absorbing ion is called a ‘sensitizer’. In many cases, the host lattice transfers its excitation energy to the activator so that the host lattice acts as the sensitizer. High-energy excitation always excites the host lattice. Direct excitation of an activator is only possible with ultraviolet and visible radiation [2].
Experimental and Characterization Techniques
Published in Amit Sachdeva, Pramod Kumar Singh, Hee Woo Rhee, Composite Materials, 2021
Rahul, Rakesh K. Sonker, P. K. Shukla, Pramod K. Singh, Zishan H. Khan
On illumination with UV-visible radiation, the atoms or molecules of the material get excited, and the atoms present in the molecules vibrate and rotate with respect to each other. The absorption of UV or visible radiation corresponds to the excitation of outer electrons. When an atom or molecule absorbs energy, electrons move from the ground state to an excited state. Only certain functional groups in a molecule are Raman active. These functional groups are called chronophers. The vibrational and rotational modes of the molecules superimpose on the absorption spectrum. Therefore, the UV-visible absorption spectra of the chromophores become complex and their careful investigation provides a lot of information regarding the sample [38].
Two-Gaussian Fitting Method for Charge Exchange Spectroscopy on Measurements of Ion Temperature and Toroidal Plasma Flow Velocity in the KSTAR Tokamak
Published in Fusion Science and Technology, 2020
In principle, random thermal velocity (or ion temperature) and plasma flow velocity can be derived from measurements of the line emission by ions in the plasma. The Doppler width and Doppler shift of the measured line-emission spectrum are applied to obtain the ion temperature and flow velocity, respectively. Since ions in the center of the plasma of high temperature are fully ionized except for heavy impurities, there is no spontaneous line emission from the ions. However, fully ionized ions can emit light by receiving electrons from neutral atoms, i.e., the charge exchange process, inside the plasma. When an ion that is fully ionized receives an electron, the electron first stays at a high quantum level. Subsequently, the electron decays from the excited state to the ground state while emitting a photon of a certain energy, or wavelength.
Fluorescent molecular tomographic reconstruction via compensating for modelling error
Published in Journal of Modern Optics, 2019
Wei Zou, Erxi Fang, Jiajun Wang, Xinyu Pan
In biomedical research, optics-based molecular imaging is the most commonly used modality for visualization (1, 2). The rapid development of NIR fluorescent markers makes fluorescent molecular tomography (FMT) a promising imaging technique, which has received particular attention (3). Great efforts have gone into evaluating the potential for such a non-invasive modality in imaging of human tissue (4–6). In the imaging modality of FMT, selective targeting and the increased vascular density may result in accumulating of injected fluorophores in the diseased tissue. NIR light is utilized to quantify the distribution of fluorophores in tissues. When a fluorescence molecule absorbs a photon, electrons in its outer shell are excited and lifted to an excited state. Upon return to the ground state, the fluorescence molecule releases energy detected as fluorescence. The measured data from detectors are used to reconstruct the distributed images of the absorption coefficient, the scattering coefficient, the fluorescent yield, and lifetime parameters. The distributions of fluorescent parameters have important applications in clinical diagnosis. FMT enables the capacity to study disease evolution and the effects of treatment (7). Furthermore, it provides lower health risks and the significant potential in medical diagnosis (8).